Patient-Specific Instrumentation Does Not Improve Alignment Compared to the Extramedullary Foot Holder for the INBONE II Total Ankle Arthroplasty.

Abstract

Background: Patient-specific instrumentation (PSI) was developed to improve accuracy and efficiency in implant placement for total ankle arthroplasty (TAA). This study represents the first to measure the accuracy of PSI regarding implant alignment and implant size in the INBONE II total ankle system (Stryker). A secondary goal was to compare radiographic and clinical outcomes between the PSI and that of a matched group of implants performed with standard instrumentation.

Methods: This retrospective study of 92 patients (46 PSI and 46 non-PSI cases matched by age and sex) was performed at a single institution between 2006 and 2024, including TAA patients with INBONE II implants. Median age was 61 years (range 27-81). Median body mass index (BMI) was 29.6 (range 19.9-45.6). One surgeon performed 71% of PSI. A different surgeon performed 96% of non-PSI cases. PSI alignment (tibiotalar angle [TTA]), deformity correction (talar-tilt [TT]), radiation exposure, tourniquet, and operative time were compared to the standard jig method (non-PSI). Total fluoroscopy, tourniquet and procedure time, and preoperative and postoperative radiographs were analyzed.

Results: PSI predicted the correct size in 67% (n = 31) of talus implants and 89% (n = 41) of tibial implants. Median absolute deviation in the mortise view was 1.3 (IQR 0.53-2.18) and 1.8 (IQR 1.35-3.5) in the lateral view. For both groups, postoperative median TTA deviation was less than 2 degrees and postoperative median TT was less than or equal to 1 degree. Median fluoroscopic time was 92.1 seconds for PSI and 104.3 seconds for non-PSI. PSI had a longer tourniquet (156.5 vs 134.5 minutes) and procedure time (188 vs 161 minutes) compared with non-PSI.

Conclusion: In this study of stemmed TAA implants, surgeons achieved alignment generally consistent with PSI predictions. PSI adequately predicted implant size. For most cases, PSI achieved similar alignment and correction of deformity compared with standard instrumentation. PSI did not improve radiographic alignment compared with traditional instrumentation and was associated with longer operative times, possibly reflecting the primary surgeon's early experience with the technique. Each surgeon should select PSI or the standard jig based on their experience and preference.